The present invention relates to a golf ball having excellent controllability and improved flight performance.
To fulfil the expectations of golf players, efforts are currently made to develop a golf ball that satisfies both the requirements of a longer distance on driver shots and good controllability on approach shots. It is known from such technical development works that the use of a soft cover is effective for improving the spin performance of a golf ball.
With respect to the controllability of a golf ball, it is described in JP-A 9-135923 that the greater the contact area between a club face and a golf ball upon impact, the better becomes the controllability of the ball.
Since these golf balls are developed primarily for improving the controllability and spin performance thereof, they are not necessarily good in flight performance and many balls are rather inferior in flight performance.
It is known from JP-A 9-135923 that the surface coverage of dimples must be reduced in order to increase the contact area of a ball with a club face. In general, a reduced number of dimples on the ball surface fail to exert desired dimple aerodynamics and render it difficult to improve the flight performance of the ball. It is then desired to have a golf ball which is improved not only in spin and controllability by increasing the contact area of the ball with a club face upon impact, but also in flight performance by taking advantage of dimple aerodynamics.
It is therefore an object of the invention to provide a golf ball which has fully adequate spin characteristics and controllability as well as improved flight performance.
It has been found that when a golf ball is formed in its surface with dimples so as to optimize the ratio A/B between the effective surface area of contact A and the apparent surface area of contact B by the golf ball with the club face when the ball is hit with a driver at a head speed of 50 m/s, and to set a dimple surface coverage above a specific level, the contact area of the ball surface with the club face is increased to ensure excellent spin and control characteristics, and satisfactory dimple effects are exerted to ensure excellent flight performance.
xe2x80x9cEffective contact area,xe2x80x9d as used herein and shown in FIG. 1, refers to the surface area of contact which accurately represents those places on the surface of the ball that actually come into contact with the club face. It excludes the scattered places in the same general region of the ball""s surface which do not actually come into contact with the club face, such as dimple recesses. xe2x80x9cApparent contact area,xe2x80x9d as shown in FIG. 3, is used herein to refer to the entire surface area of the general region of the ball that comes into contact with the club face. This quantity includes scattered places within this region where the surface of the ball does not actually come into contact with the club face, such as dimple recesses. That is, when a circular or elliptical region of the ball contacts the club face, the surface area of this circular or elliptical region is the apparent contact area. Subtracting from this apparent contact area the surface area of those places such as dimple recesses where the surface of the ball does not actually come into contact with the club face yields the effective contact area.
Mention is made of xe2x80x9ccontact areaxe2x80x9d in JP-A 7-112036, or example. However, the xe2x80x9ccontact areaxe2x80x9d in these patent references denotes the overall surface area computed by such means as elliptical approximation or blacking in of the general region of contact on the ball. This has the same meaning as apparent contact area B used in the present invention, but differs in meaning from effective contact area A as used herein.
More particularly, when a golf ball is actually hit with a club at a certain initial velocity, the feel of the ball to the player is correlated to the contact area of the ball with the club face upon impact as described in JP-A 7-112036 etc. The xe2x80x9ccontact areaxe2x80x9d described in these patent references does not accurately represent the area of the ball in close contact with the club face because the dimples which are out of contact with the club face are not taken into account. This contact area corresponds to the apparent contact area B as used herein. The inventor paid attention to the effective contact area of the ball in actual contact with the club face and the apparent contact area as described in the patent references. It has been found that when a golf ball is manufactured such that the ratio of effective contact area A to apparent contact area B may range from 0.40 to 0.60 and the xe2x80x9cdimple surface coveragexe2x80x9d (the percent of the ball""s surface covered by the dimples formed thereon) may be at least 71%, not only spin and control characteristics are improved, but also flight performance is enhanced.
Therefore, the invention provides a golf ball comprising a core and a cover that encloses the core and bearing a number of dimples in its surface. The ball, when hit with a driver having a club face at a head speed of 50 m/s, has an effective contact area A and an apparent contact area B with the club face such that the value of A/B is from 0.40 to 0.60. The ball has a dimple surface coverage of at least 71%.